Summary: A critical component of a biologics license application is the description of the validation of analytical methods and the establishment of specifications for the product subject of the application and its intermediates obtained during manufacturing. The Laboratory of Methods Development and Quality Control (LMDQC) is a resource of the Division of Bacterial, Parasitic and Allergenic Products (DBPAP). LMDQC works with other laboratories within DBPAP and with the sponsor to ensure the timely development of standardized tests for the quality assessment of bacterial products. Additionally, during the methods development process, needs for reference materials are identified and production and standardization of materials is coordinated. FY2001 activities: Clinical evaluations of the efficacy of diphtheria toxoid vaccines are based on measurement of the toxin-neutralizing serum antibodies. An investigation of the Vero cell culture method, an assay commonly used to measure diphtheria toxin-neutralizing antibodies in human sera, was initiated in an effort to improve standardization. Approaches to improving the quantitation of the Vero cell assay through improved procedures for determining end-points and calculating results are being evaluated. Results in the Vero cell assay are being compared to an in vivo guinea-pig skin neutralization (Lr) test for national and international reference sera and representative human sera.